Electronic devices may not operate properly if a voltage level of a power supply drops below a predetermined threshold. FIG. 1 shows a schematic diagram of a conventional under-voltage detection circuit 100. The under-voltage detection circuit 100 can include a bandgap circuit 102, a voltage comparator 104, and a voltage divider 106. The bandgap circuit 102 can generate a reference bandgap voltage which remains substantially constant if temperature varies. The voltage divider 106 receives an input voltage VIN, and provides a sense voltage proportional to the input voltage VIN at a node 108. The voltage comparator 104 compares the sense voltage to the reference bandgap voltage, and generates a detection signal UVA indicating an under-voltage condition if the sense voltage is less than the reference bandgap voltage. However, since a level of a current flowing through the voltage divider 106 is proportional to a level of the input voltage VIN, power consumption of the under-voltage detection circuit 100 may be increased when the input voltage VIN is increased.
FIG. 2 shows a schematic diagram of another conventional under-voltage detection circuit 200. The under-voltage detection circuit 200 includes a current generator 208 and a voltage comparator 204. The current generator 208 generates a current proportional to temperature (e.g., absolute temperature) of the under-voltage detection circuit 200. A first bandgap voltage generator constituted by a bipolar transistor Q2 and a resistor R3 can receive the current and can provide a first bandgap voltage accordingly. Similarly, a second bandgap voltage generator constituted by a bipolar transistor Q6 and a resistor R2 can provide a second bandgap voltage. Therefore, a sense voltage, e.g., equal to the input voltage VIN minus the first bandgap voltage, is obtained at a node 202. A threshold voltage, e.g., equal to the second bandgap voltage, is obtained at a node 201. The voltage comparator 204 generates a detection signal UVA indicating an under-voltage condition if the sense voltage is less than the threshold voltage.
However, the voltage comparator, e.g., the voltage comparator 104 or 204, may increase the complexity and cost of the under-voltage detection circuit 100 or 200. Moreover, oscillations of the under-voltage detection circuit 100 or 200 may be triggered. For example, if the sense voltage is increased to be greater than the threshold voltage and then decreased to be less than the threshold voltage in a relatively short time period, e.g., caused by noise of the under-voltage detection circuit, the detection signal UVA may oscillate between two states, e.g., a high electrical level and a low electrical level. Thus, stability of the under-voltage detection circuit 100 or 200 may be decreased.